NOT APPLICABLE
NOT APPLICABLE
NOT APPLICABLE
The present invention relates generally to the field of power distribution systems for telecommunication networks and specifically to a system and method for reducing power dissipation by regulating voltage supplied to multiple telephone line driver circuits.
In a plain old telephone service (POTS) system, the central office (CO) is typically equipped with racks of shelves containing multiple line interface circuits or line driver circuits (LDs). Each of these circuits is connected to drive a telephone line or loop, the other end of which ultimately connects with subscriber telephone equipment. A power supply voltage applied to the LDs at the CO typically has a wide range. It may vary from a level representing the minimum value required to provide service, to a maximum that can be significantly higher. Voltage in excess of an optimum value is either applied to the telephone loop or, more often, dropped across the LD. Either way, this excess voltage is generally dissipated as heat and represents lost power from the supply. With increased demand to deliver a higher number of POTS LDs in a smaller shelf space, there is a corresponding need to reduce the power dissipation of these LDs to avoid both overheating and unnecessary power loss.
For a typical twisted-pair copper subscriber loop, the direct current (DC) electrical characteristics of the loop are specified by industry standards, and lie within defined ranges. In order to provide continuing telephone service in the event of an alternating current (AC) mains power failure, batteries are often provided at the CO for backup. The minimum battery voltage that is required to provide service within industry specifications depends on the LD circuitry. For a typical LD card servicing a subscriber loop, the minimum Tip to Ring voltage requirement at the LD output terminals is approximately 39 VDC on the longest loops, but may be lower for shorter loops as will be appreciated by a person skilled in the art. A corresponding voltage range for CO batteries in POTS applications generally ranges between 42 and 65 VDC.
As an alternative to batteries, some multi-line POTS applications use a DC power supply to deliver an equivalent to battery voltage. In such cases, the output voltage fluctuation or regulation of these DC power supplies is generally less stringent than for other, non-POTS applications. This reduced regulation allows the voltage input to the LDs to vary considerably, allowing for a corresponding voltage variation at the output terminals of the LDs.
As previously mentioned, battery voltage in excess of that required by a LD to provide an industry standard level of service may be applied either directly to the loop resulting in higher power dissipation within the loop, or across the LD. Thus, as voltage fluctuates above the required level, there is excessive power dissipation. One solution to address this power dissipation problem is to limit the current that is delivered to each loop on a loop-by-loop basis. As a result of this current limiting function, excess battery voltage is not dropped in the loop. However, a portion of the excess battery voltage continues to be dropped across the LD.
The following are some prior art attempts to reduce the power dissipation. U.S. Pat. No. 5,754,644 (Akhteruzzaman) describes a method for controlling power losses associated with the operation of LDs. For each LD, a detected loop current is used to access a threshold voltage value from a database. A threshold voltage based on the threshold voltage value retrieved from the database is compared to a feedback voltage for controlling the duty cycle of a switching converter circuit in the LD. Controlling the duty cycle of this switching converter circuit enables control of battery voltages based on the comparison of the threshold voltage and the feedback voltage. The battery voltage for each LD is then set at the minimum voltage needed to provide the required loop current. Similarly, U.S. Pat. No. 5,737,411 (Apfel et al.) describes a system wherein the LD for a given loop selects between two battery voltages to be applied to the loop depending on the status of the loop, for example either on or off hook. Comparable systems and methods for reducing power losses on an individual LD or loop basis are described in U.S. Pat. Nos. 5,960,075 (Sutherland et al.), 5,815,569 (Akhteruzzaman), 5,596,637 (Pasetti et al.), and 4,704,670 (Gradl et al.).
However, the systems described by the patents listed above can be complex and relatively expensive to implement. Further, the systems consume area on a line card, of which there is typically little to spare. Therefore, it is an object of the present invention to provide a system and method for reducing power dissipation in line drivers that obviates or mitigates the above mentioned disadvantages.
In accordance with an aspect of the invention, there is provided a system for reducing power dissipation in a plurality of line driver circuits. The system comprises a power source for providing a voltage source for the plurality of line driver circuits and a voltage regulator coupled between the power source and the plurality of line driver circuits. The voltage regulator receives an output of the power source and provides a constant predefined voltage to an input of the plurality of line driver circuits. Having a constant predefined voltage input to the plurality of line driver circuits reduces their average power dissipation.
In accordance with another aspect of the invention, a method of reducing power dissipation in telecommunication networks is provided. The method includes interposing of a single highly efficient voltage regulator between the battery or power supply and multiple LDs components of the telecommunication network""s power distribution system. When the voltage regulator is used rather than or in addition to voltage regulator circuitry in each LD, the power dissipation in both the LDs and the power distribution system may be reduced.